Snap acting device



July 14, 1942 l.. w. BURcH Y 2,290,093

SNAP ACTING' DEVICE Filed oct. :51, 19,39

INVENTOR @a W /mli @M24/Mu ATTORNEY5 l Patented July 14, '1,942

SNAP ACTING DEVICE Lyndon W. Burch, Pelham, N. Y., assignor to The Wilcolator Company, Newark, N. J., a corporation of Delaware Application october a1, 1939, serial No. 392,124

4 Claims. (Cl. 25W-:8)

-This invention relates to snap acting devices and more particularly to a,novel device of this type which includes a dished snap element o perable to produce a snap action at one end or at both ends and in which the snap element and its actuating means may be included in a unitary and compact assembly. The new device is of simple construction and may be made at low cost.

One feature of the present invention resides in the provision of a novel snap mechanism in which the snap element is made from a sheet of spring metal having a dished shape and is arranged to provide a snap movement at one end or at both ends when actuated.

According to the invention,'I provide abutment means engaging the convex face of the element between its ends, and abutment means engaging the concave face outwardly from the first abutment means and on opposite sides of the longitudinal axis of the element. The two on the snap' element and thereby cause actuaabutment'means are movable relatively toward` 1 each other to reduce the curvature of the snap element along its transverse axis, and when this curvature is reduced to the extent that the snap element becomes unstable, the latter snaps to a position -of opposite curvature whereby its 'ends move quickly in'a, direction generally normal to the surface offthe element. If desired, the snap element may bemade self-recovering by forming it with an accentuated curvature or permanent strain along one axis so that it`tends to return to an initial position` under the action of to the snap element to effect its movement in both directions. l

Another feature of the invention resides in the provision of la novel snap action mechanism including a double-ended snap element operable by a thermostatthroughv an adjustable connection, all of the parts being included in a unitary assembly. In one form of the mechanism, the

snap element is seated on one side of a supporting member and is Aengagedon its convex side by a pressure plate. The endsof the pressureplate may-bey offset to support the ends of .a bimetallic l l t compensator, the pressure plate and v com- 55. sult. the effectiveperlmeter of the sheet is retion of the latter. By adjusting the rod, the temperature at which the thermo-responsive means actuates the snap'element may be varied.

These and other features of the `invention may be better understood'by reference to the following detailed description taken in conjunction with thev accompanyingV drawing, in` which lFig. 1 isva vtransverse sectional view ol o'ne form ofthe new snap mechanism, showing the snap element in its iiexed position;

Fig. 2 is a similar view showing the' snap element in its normal position, parts of the mecha-- Fig. 5 is a plan view of the snap element shown in Figs. l to 4, inclusive;

Figs. 6 and A'I are longitudinal and transverse sectional views, respectively, of the snap element;

Fig. 8 is a sectional view on the line 8-8 in F1s.5:

Figs. 9 and l0 parts of the device shown in Figs. 1 to 4, inclusive, and

Fig. 11' is a plan/view of a modiiled form of the snap element.

Referring to the drawing,4 the snap mechanisin illustrated comprises a snap element 20 made from a sheet oi spring metal which, as shown, is generally rectangular in form. 'Radiating fromv the central portion of the sheet toward 'the corners thereof are slots 2| ter minating a short distance inwardly from the corners. The' metal between the outer end of .each slot and the adjacent corner is crimped, as shownat 22, so that the outerportion -ot Vthe-sheet is drawn in or gathered. Asfare'- 'are datan views of' different` I the supportingv plate.

duced and the sheet is caused to assume a dished shape. Preferably, the lengthwise curvature of the sheet is increased beyond that resulting from the gathering ofthe metal at the corners,

lpart tot the subject tial position in which its ends are depressed. When the rod 34 is rotated to screw it into the pin 35, the head of the latter is raised from the end of V the bellows against the action of spring 5 36. At the same time, the pressureof shoulder 31 on the retaining member is increased, and this increased pressure is transmitted through the compensator and the pressure plate to the snap element, whereby the curvature of the snap l element is reduced until the element reaches an matter of my copending application, No.'325,979, l

filed Mar. 26, 1940, which is a continuation-inpart of thel present application.

. The snap element may be exed by any suit-y able means to force it to a position of /opposite curvature. In the drawing, I have shown a prel. ferred form of exing means comprising a supporting plate 23 on which a pair of headed pins 24 are" mounted, the pins extending upwardly through openings 25 located near the sides of the snap element on the transverse laxis thereof. Thus, the heads of the pins 2t act as seats engaglng the normally concave side of the'snap element, and the shanks of vthe pins serve to locate the snap element relative to the supporting plate. On top of -the snap element is a pressure plate 26 having. spacd abutments 21 engaging 'the normally convex side of the snap element inwardly from the pins g4. The pressure plate is formed with openings 23 through which the shanks of the pins extend, and surrounding the openings are bosses 23 adapted to be engaged by the snap element. 'I'he ends of the pressure plate are offset and reduced, as shown at 33, and mounted on these ends is a bimetallic compensator 3l which is likewise provided with reduced.

ends 3| seated on the endsof the pressure plate. The compensator is held in position on the pressure plate by a U-shaped retaining member 32 having slots in the` legs thereof for receiving the reduced ends of the compensator and pressure plate. Lugs 3 project from the supporting plate through openings in the legs of the retaining member and serve to secure the latter to An adjustment rod 34' extends through openings in the retainer 32 and the compensator and through aligned openings in the pressure plate, the snap element and the supporting plate, the

rod being threaded at its lower end into a headed pin 35. A spring 36 is coiled around the pin 35 between the head thereof and the supporting plate 33, andthe spring urges the pin and rod downwardly so as'to hold'a shoulder 31 on the rod in engagement with the retaining member 32.

The pin 3 5 is movable by a thermo-responsive assembly mounted on the side of the supporting plate ^23 remote from the snap element. This assembly,1 .as shown, comprises a cup-shapedV member 33 secured `at its open yend to the supporting plate and containing a metallic bellows 33 sealed at itsjopen end to an annulus 40, whereby the bellows,.the annulus and the cup- ,shaped member define an expansible and con-,- tractible chamber Il. A capillary tube I2 leads from this chamber to a bulb, not shown, and the bulb, tubeand chamber may be filled with a 'unstable position and finally snaps over to af .position of opposite curvature, as shown in Figs. 1 and 3. D uring this snap action,the sides of the snap element move upwardly against the l5 bosses-4 29 through a small amplitude, but the y much greater amplitude.

ends of the element move upwardly through a The snap movement thus producedvat the ends of the element may beused .to actuate a pair of independent control means, such as valves or switches, one for each end of the element.

Assuming, for example, that this snap movement is used for closing a pair of switches to supply heat to an oven, the bulbat the end of tube 42 ,is disposed in the oven so that the liquid in the bulbexpands as the oven temperature rises. This expansion of the liquid acts to contract the bellows 33 until the end thereof en-f gages pin 35. Thereafter, continued contraction of the bellows moves the pin 35 and the rod 34 upwardly against the action o f spring 36 and thereby relieves the pressure exerted on the snap element by shoulder 31, compensator 3| and pressure plate 26. When this pressureis relieved suiciently, the snap element moves quickly back to its initial, switch-'opening position due to the permanent strain in the sheet 20 tending to return\it to this position. As the oven cools, the

thermo-responsive liquid contracts and allows 40 the bellows to expand un'derthe action of spring 36, with the result that the pin 35 and rod 34 are moved downwardly to increase the pressure on the snap element and the latter vis eventually caused to snap back to its switch-closing position'. Thus, the snap element moves back and forth so'as to maintain a substantially constant' temperaturein the o ven, By turning the rod 3l to different angular positions, the location "of the screw 35 relative to the bellows and there- 5o fore thetemperature at which the bellows oper- .,ates the snap element may be. varied. v

'I'he new snap mechanism is simple Vand compact in construction, and the component parts comprisingthe snap element, the pressure plate,

the thermo-responsive means and compensator,

and the temperature adjustment means are included in a unitary assembly. Ihe ends of the snap element move quickly through a relatively great amplitude, and' by varying the length of the snap element the amplitude may be increasedJordecreased. It will be observed that,

as the pressure plate. 26 moves downwardly from the position' shown iii Fig. 2 to reduce/"the curvature of the snap element, the bosses 29 on the 5 plate approach the seats for the snap element thermo-responsive liquid, such as chlorinated di' phenyl, so that the bellows will expand .and contract'as a result of thermal expansion and contraction of the liquid in the bulli Y In the normal position. of the parts' shown in Figs. 2 and 4, the pressure exerted on the snap on the pins 24, and just as the snap action takes place the bosses engage the surface of the snap element and prevent any substantial movement of its sides Jbetween the pressure plate andl the heads of the pins.

Ii' onlya single action snap mechanism is desired, 'the snap element shown in Fig. 11 may be employed.. As there shown, the snap element is made from a -relatively 'short piece of spring 75, metal M provided with a pair of slots I5 radiating from the central partof the element toward adjacent corners there i. The metal between the end of each slot'an the adjacent corner is crimped, as shown at 46, to shorten the effective perimeter of the snap element and force it into a dished-shape. The snap elenient may be provided with a permanent strain so that it is selfrecovering, andy it may be formed near the end opposite the crimped portions 46 with an opening 41 for receiving the threaded pin 35 and with holes 48 -for receiving the pins 24. t

The new snap acting device' is particularly element, a pressure plate engaging the opposite face of the snap element and having openings for receiving the pins, a iiexible retainer releasably secured to the support and holding the plate. and snap element in pressure transmitting relation on the support in a unitary assembly, whereby the plate and snap element are removable irom the support on release of the retainer, thermo-responsive means mounted on the support, and an adjustable connection between said means and the pressure plate and extending through the adapted for use on electric ranges for operating v thermo-responsive iluid in the expansible and contractible chamber 4| may be subjected to heat from one or more of the open heaters. This extraneous heat would impair the accuracy of the oven control unless suitable provision were made to counteract its effect. In the new construction, any changes in the temperature adjacent the snap mechanism are counteracted by flexing of the compensator 3l relative to the pressure plate 26. That is, if the temperature should rise and heat the liquid in chamber 4I so as to collapse the bellows, the compensator 3i ilexes and moves its ends downwardly to increase the pressure on plate 26, whereby the tendency for rod 34 to move upwardly on collapsing of the bellows is counteracted. Conversely, if the temperature adjacent the snap mechanism decreases, the compensator 3| exes in the opposite direction and tends to relieve the pressure on the plate 26.

I claim:

1. A unitary, compensating. thernfo-responsive snap acting device comprising a snap elesnap element engaging one face thereof, pressure and compensating members adjacent the opposite face of the snap element, said members being 'seated one 'against the other and one of the members engaging said second face of thesnap element, a exible retainer releasably secured to the support and holding said memrelation on the support lin a unitary'assembly,

.bers and snap element in pressure transmitting whereby'said members and snap element are removable from the support on release of the retainer, thermo-responsive means mounted on the support, and an adjustable connection between said means and the other of said members and extending through the support, the snap element and said members.

support, the snap element and the plate; said pins being operable to maintain the pressure plate, the snap element and said connection in centered relation on the support during operation of the snap element by' said means.

3. A unitary, compensating, thermo-responsive snap acting device comprising a snap element having a dished shape, a support for the snap element engaging one face thereof, a pressure plate engaging the opposite' face of the snap element and having its ends offset away from the snap element, a bimetallic compensator engaged at its ends with said offset ends of the plate, the intermediate portion of the compensator being free to flex relative to the plate, a flexible re.

tainer releasably secured to the support and receiving said'ends of the compensator and plate for holding they compensator, the-plate and the snap element in pressure transmitting relation on the support in a unitary assembly. whereby the compensator, the plate and 'the snap element are removable from the support on release of the retainer, thermo-responsive -means\mounted on the support, and'an adjustable conneotionbetween Y said means and the compensator and extending through the support, the snap element, the plate `and the compensator.

. tion of the compensating member and having 2. A unitary, thermo-responsive snap acting snap element and engaging one face thereoiat" spaced points, between the opposite edges ofthe' openings in its legs for receiving said ends of the compensatingiand pressure members, the legs being secured near their ends to the support and holding the snapelement and said members on the support in a unitary assembly, thermo-responsive means mounted'on the support, and an adjustable connection between said means and the central portion' of the retainer and extending through the support, `the snap element and said members.

LYNDGN W. BURCH. 

